Temporomandibular disorders (TMD) are one of the main sources of non-dental head and neck pain. Its pathology is not entirely understood, and its etiology is complicated. Over time, orthodontists have been more interested in relationship between occlusal variables, orthodontic therapy, & TMD, and patient awareness and interest in oral health have expanded. Therefore, the purpose of this book is to give a brief knowledge of the temporomandibular joint's anatomy, TMD, and their complex etiology as well as their function in orthodontics.